Making 2-D Materials Mechanochemically by Twin-Screw Extrusion: Continuous Exfoliation of Graphite to Multi-Layered Graphene

Mechanochemistry has developed rapidly in recent years for efficient chemicals and materials synthesis. Twin screw extrusion (TSE) is a particularly promising technique in this regard because of its continuous and scalable nature. A key aspect of TSE is that it provides high shear and mixing. Because of the high shear, it potentially also offers a way to delaminate 2-D materials. Indeed, the synthesis of 2-D materials in a scalable and continuous manor remains a challenge in their industrialization. Here, as a proof-of-principle, the automated, continuous mechanochemical exfoliation of graphite to give multi-layer graphene (MLG, ≈6 layers) by TSE is demonstrated. To achieve this, a solid-and-liquid-assisted extrusion (SLAE) process is developed in which organic additives such as pyrene are rendered liquid due to the high temperatures used, to assist with the exfoliation, and simultaneously solid sodium chloride is used as a grinding aid. This gave MLG in high yield (25 wt%) with a short residence time (8 min) and notably with negligible evidence for structural deterioration (defects or oxidation).